The prior art is well developed in the field of gas separations using adsorptive beds, wherein a more selectively adsorbed key gas specie is retained on the beds while a less selectively adsorbed secondary gas specie is allowed to pass through the bed. Adsorptive separation techniques allow for the separation and recovery of an individual product, dual products, or potentially in combination with a complex arrangement of adsorptive beds, multiple products can be obtained.
Various techniques for separation of air to recover nitrogen, oxygen or nitrogen and oxygen are known in the prior art.
In U.S. Pat. No. 4,013,429 a process is set forth for the adsorptive separation of air using two parallel sets of beds including pretreatment beds for the removal of water and carbon dioxide and main beds for the selective adsorption of nitrogen product. This process utilizes a series of pressure or volume variable receiving vessels, which constitute an expense and an operational liability. In addition, this process utilizes both compressors and vacuum pumps, which require power input for both. Finally, the process utilizes segregated pretreatment and main beds for differential regeneration.
A similar system is disclosed in U.S. Pat. No. 3,957,463. This process is for recovery of oxygen. The process requires an expansible oxygen receiver, as well as compression feed equipment and vacuum desorption equipment.
In U.S. Pat. No. 4,144,038 an adsorptive separation of argon, which is unadsorbed, from adsorbed oxygen and nitrogen is performed in a process which precludes the use of rinse or purge gas and performs feed by the vacuum of an unadsorbed product compressor at the effluent end of the adsorptive beds.
In U.S. Pat. No. 4,264,340, a process is disclosed for the recovery of product nitrogen which has been dried and cleaned of carbon dioxide and hydrocarbons. Again, compression feed, vacuum recovery and expansible receivers are an integral part of the process.
In addition various techniques are known for separating carbon oxides from impurities or other product quality gases as identified in U.S. Pat. Nos. 4,770,676; 4,705,541; 4,000,990 and 4,077,779.
The present invention overcomes the disadvantages of the prior art by avoiding power consumption of feed gas compression and the need for capital intensive and operational limiting storage vessels in a process as will be set forth below utilizing vacuum swing adsorption.